A currently available disk that is used with a disk player for recording and playing back information with a light beam is fabricated as follows. First, pregrooves that act as storage tracks are formed. Then, identifying signals, such as address signals indicative of the addresses of the pregrooves, are recorded in the pregrooves in the form of ridges, depressions, or reflectivity variations. This conventional recordable disk is described further detail with reference to FIG. 1.
Referring to FIG. 1, the aforementioned disk that allows information to be written onto, or read from, the disk is indicated by numeral 1. Tracks P storing information are so formed on the disk that they lie in circles or spirals around the center of the disk. The circles or spirals are uniformly spaced from one another. Pregrooves 2 are formed along the tracks P. Address signals indicating the addresses of the pregrooves 2 are recorded in the form of discrerte depressions 3 or ridges in the pregrooves, one depression 3 per turn of pregroove 2. Some depressions 3 are also shown in FIG. 1 on an enlarged scale.
The pregrooves 2 are generally radially spaced about 1.6 microns from one another. The pregrooves 2 have a width of about 0.7 micron and a height of about 0.8 micron. Although the pregrooves 2 are shown to be microscopic depressions, microscopic ridges or protrusions may be formed instead.
FIG. 2 shows the pits corresponding to signals and the depressions corresponding to address signals on an enlarged scale, the pits being recorded in the pregrooves 2 of the storage tracks P.sub.1 -P.sub.3. The pits, indicated by numeral 4, corresponding to the signals are formed by illuminating the disk with a laser beam while rotating the disk 1. The laser beam is modulated with a signal to be recorded. The surfaces in the pregrooves which store information are made to exhibit variations in the reflectivity, for example, by the formation of the pits 4. The depressions 3 corresponding to address signals are discrete similarly to the pregrooves. Also, ridges or protrusions may be formed instead of the depressions 3. The pits 4 and depressions 3 are read by a laser beam 5 focused on the disk. Since the pits 4 are substantially narrower than the depressions 3, when any one track of the pregrooves 2, for example, the pits 4 formed in the pregrooves P.sub.2, is read, it is hardly likely that the laser beam 5 will hit the pits 4 in a neighboring track P.sub.1 or P.sub.3. Hence, the level of crosstalk which is produced between neighboring pregrooves and which is introduced into the reproduced signals is not so high as to present problems. However, the depressions 3 corresponding to address signals have a larger width. Therefore, it is very likely that the laser beam 5 will strike the depressions of neighboring tracks. Another problem arises from the fact that a considerable amount of crosstalk is produced, because address signals are recorded on the disk as changed in geometrical shape, such as depressions or ridges. For these reasons, the conventional disk has posed some problems. That is, in the conventional recordable disk, the depressions 3 corresponding to address signals are formed in neighboring positions on the storage tracks on the disk 1 and, therefore, crosstalk is always produced between the depressions 3 in neighboring tracks. This crosstalk increases the amount of noise contained in the reproduced address signal, i.e., the signal-to-noise ratio deteriorates. As a result, a large quantity of error is produced in reading information. This has created a great problem when the recordable disk is used.